Frequency conversion in near-stoichiometric lithium tantalate fabricated by vapor transport equilibration

Frequency conversion using quasi-phasematched (QPM) nonlinear devices is efficient and engineerable. One method of quasi-phasematching can be realized by periodically poling ferroelectrics. Lithium tantalate, like many ferroelectrics, is limited in application by photorefractive damage (PRD) in the commonly available, congruently melting composition. Vapor-transport-equilibrated, near-stoichiometric lithium tantalate (VLT) has been shown to have reduced defect concentrations and increased photoconductivity. Because of the two-order of magnitude increase in photoconductivity, VLT has improved resistance to PRD and has been used to demonstrate efficient and stable frequency conversion at high average powers. QPM devices based on VLT have allowed the demonstration of near room-temperature generation of visible light. Generation of 10 W of CW 532-nm radiation by second harmonic generation from 29 W of 1064-nm radiation has been demonstrated in a 4-cm-long device. Devices periodically poled for generation of 589-nm radiation by both second harmonic and sum frequency generation have also been demonstrated as near room temperature, multi-watt sources. Control of the ferroelectric properties allowed periodic poling down to a period of 5 microns, suitable for generation of 458.3-nm radiation by second harmonic generation. Investigations into the application of periodic poling and vapor transport equilibration on rotated-cut VLT crystals have led to the development of aperture-scalable, quasi-phasematched devices suitable for high peak- and average-power nonlinear optics.